                Patent Document 1: Japanese Patent Laid Open No.1994-114037        Patent Document 2: Japanese Patent Laid Open No.1993-212093        Patent Document 3: Japanese Patent Laid Open No.1995-289504        
In the Patent Document 1, a medical capsule which has plural capsules running along one guide wire inserted into a body cavity is disclosed. This is provided with a roller to tuck the guide wire in the capsule and a micro motor to drive the roller. The driven roller runs the capsule by the reactive force obtained from the guide wire. Further in the Patent Document 1, it is disclosed that plural pairs of electromagnets are provided on the each facing edge of the capsule in order to remote control the mutual angle between the capsules by magnetizing any of the electromagnet.
In the Patent Document 2, a medical capsule is disclosed, in which forward traveling legs and backward traveling legs, a bimorph transducer to vibrate the traveling legs, and covers to cover those traveling legs are provided. This capsule can move backward by covering the forward traveling legs with the cover to make the backward traveling legs only effective while the forward and the backward traveling legs are both activated. Similarly, it can move forward by covering the backward traveling legs with the cover.
In the Patent Document 3, a capsule endoscope unit is disclosed, in which balloons are provided front and rear and a self-advancing part connecting those balloons with retractable bellows.
The self-advancing part expands, for example, the front balloon to fix it to the inside wall of duodena etc., and deflate the rear balloon, and then retract the bellows to move the rear balloon forward.
Next, it expands the rear balloon to fix it to the inside wall, and deflate the front balloon, and then extend the front balloon to move the front balloon forward. By repeating this sequential process, it can move forward intermittently. Further, the self-advancing part can move backward by carrying out the sequential process in reverse.